Coated, antimicrobial, chemically strengthened glass and method of making

ABSTRACT

The disclosure is directed to a chemically strengthened glass having antimicrobial properties and to a method of making such glass. In particular, the disclosure is directed to a chemically strengthened glass with antimicrobial properties and with a low surface energy coating on the glass that does not interfere with the antimicrobial properties of the glass. The antimicrobial has an Ag ion concentration on the surface in the range of greater than zero to 0.047 μg/cm 2 . The glass has particular applications as antimicrobial shelving, table tops and other applications in hospitals, laboratories and other institutions handling biological substances, where color in the glass is not a consideration.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/197,312, titled “Coated, Antimicrobial, Chemically Strengthened Glassand Method of Making” filed Aug. 3, 2011, which claims benefit ofpriority under 35 U.S.C. §119 of U.S. Provisional Application Ser. No.61/371,364 titled “Functionally Coated Antibacterial, ChemicallyStrengthened Glass and Method of Making” filed Aug. 6, 2010 and U.S.Provisional Application No. 61/510,245 “Functionally Coated,Antimicrobial, Chemically Strengthened Glass and Method of Making” filedJul. 21, 2011 the content of which are s relied upon and incorporatedherein by reference in their entirety.

FIELD

The disclosure is directed to a chemically strengthened glass havingantimicrobial properties and method of making such glass. In particular,the disclosure is directed to a colorless transparent chemicallystrengthened glass with antimicrobial properties and with a functionalcoating on the glass that does not interfere with the antimicrobialproperties of the glass.

BACKGROUND

The “health properties” of metallic silver (that is, its antiseptic,antibacterial, antiviral, antimicrobial effects) was known for centuriesbefore knowledge of bacteria, viruses and microbes generally evenexisted. In antiquity (Hippocrates of Cos and Galen of Pergamum, bothphysicians), and well through the Middle Ages, silver vessels were usedin the care of those who were ill and wounded. For example, E. Bradfordin “The Great Siege [Malta, 1565]” (New York, Harcourt, Brace & WorldInc., 1961, pp. 190-191) describes the practices of the Knights of theOrder of St. John, who were hospitalers, at Malta as:

-   -   “Simple though their surgery was and ignorant though they were        in many ways, they did at least understand the rudiments of        hygiene. In the hospital, where under normal conditions both        rich and poor, Knight and commoner, were served off silver        plate—to increase “the decorum of the hospital and the        cleanliness of the sick”—some attempt was made, even during the        siege, to look after the patients properly.” [Emphasis added.        Internal quotation from Francisco Balbi de Correggio, “La        verdadera relacion de todo lo que el ano de MDLXV ha succedido        en la Isla de Malta,′ (Barcelona, 1568)].

It was later discovered that the actual bactericide was not the metallicsilver, but the silver ions on the surface of the bulk metallic silver.Thus, the beneficial effect of using silver vessels may be attributableto the migration of silver ions from the bulk silver to the food anddrink that was consumed. With the knowledge that silver ions were areactual “antiseptic,” solutions of certain silver salts (e.g. silvernitrate) that are readily soluble in water were used as an antisepticand bactericide for many decades. Until the 1980s, dilute silver nitrateeye drops were placed in the eyes of newborns to prevent neonatalconjunctivitis, which could lead to blindness in the newborn, which mayoccur after birth. (This practice has generally been discontinued infavor of the use of erythromycin ointment).

Recently, the use both metallic silver particles and silver salts havebeen described in the patent and technical literature as a means forimparting antibacterial properties to a variety of materials such asyarns, fabrics, glass and other materials. Yahoo Lv et al. (Polymers forAdvanced Technologies, Vol. 19 (1008), pages 1455-1460) have shown thatsilver (Ag⁰) nano-particles coated on a glass slide haveantibacterial/antiviral properties resulting from close attachment ofthe nano-particles with the bacterial cells. The principle activity ofsilver (0) particles is due to the production of silver ions within anaqueous matrix containing the bacteria. Di Nunzio et al in WO2006/058906 describe prosthetic devices or implants having at least asurface layer or a part thereof (that is, an element of the prostheticdevice or implant) made of a glass, glass-ceramic or ceramic materialcontaining ions exchangeable with silver ions, and subjecting the device“to a silver ion containing aqueous solution ion-exchange process,” [idat the Abstract]. Di Nunzio et al., J. European Ceramic Society Vol. 24(2004), pages 2935-2942, discuss bioactive glasses containing silver ontheir surface that were produced by ion-exchange from dilute silvernitrate melts. Verne et al, J. Material Science; Materials Medicine Vol.20 (2009), pages 733-740, present test results of the surface doping ofbiocompatible glass that was described in WO 2006/058906. U.S. Pat. No.7,232,777 describes yarns and fabrics having an antimicrobial silverparticulate finish.

Silver ions do not possess a single mode of action. They interact with awide range of molecular processes within microorganisms resulting in arange of effects from inhibition of growth and loss of infectivity tocell death (cytotoxicity). The mechanism depends on both theconcentration of silver ions that are present and the sensitivity of themicrobial species to the silver ions. Contact time, temperature, pH andthe presence of free water all impact on both the rate and extent ofantimicrobial activity. However, the spectrum of activity is very wideand the development of resistance relatively low, especially in clinicalsituations. Silver ions are known to be effective against some 650 typesof bacteria.

The prevalence of “touch screens” in contemporary society gives rise tomany surfaces that can harbor microbes, bacteria and viruses, and thesemicrobes can be transferred from person to person. The presentdisclosure is directed to glass surfaces and to the application of theantimicrobial properties of silver ions to glasses such as the coverglasses used on many modern devices, for example, ATMs, touch screencomputers, cellphones, electronic book readers, and similar devices.

SUMMARY

This disclosure is directed to a making a chemically strengthened glasshaving antimicrobial properties and to methods of making such glass. Inone embodiment the disclosure is directed to a colorless transparentchemically strengthened glass with both antimicrobial properties and afunctional coating on the glass that does not interfere with theproperties of the glass. The functional coating is used to impart easycleanability to the surface and is generally a hydrophobic coating. Thetask of creating a chemically strengthened glass having antimicrobialproperties and having a functional coating on the glass is notstraightforward due to the fact that there are numerous other requiredproperties of the cover glass that must be maintained while trying toincorporate the antimicrobial property. It should also be understoodthat the interaction of the Ag-ion with the bacteria is restricted tothe surface of the glass, so the pertinent characterization of theconcentration needs to be expressed as per unit area. The reporting ofthe volume concentration at some interior point away from the surface,for example, >5 nm is of little consequence since the mobility of Ag⁺¹at room temperature is negligible.

Another embodiment the disclosure is directed to a method of making achemically strengthened glass having silver ions (Ag⁺¹) on the surfaceof the glass. There have been proposals to utilize a one-step (1-step)method in which an ion-exchange bath containing both a silver compoundand an ion-exchanging alkali metal compound whose ions are larger thanthe alkali metal ions in the article into which they be exchanged, andusing such bath exchange both Ag ions and the larger ions into the glassin a single step to form a chemically strengthened, silver containingglass having a compressive stress. For example, in addition to thesilver ions, the alkali metal ions that are exchanged into the glass arepotassium ions (K⁺¹). Prior art and our experiments show that the 1-stepion-exchanging bath consisting of potassium nitrate containing silvernitrate in an amount in the range of 0.01 wt % to 5 wt % where the ionexchange temperatures are typically at 300-500° C. with ion exchangetimes of >3 hours exhibits distinct disadvantages. The most significantdisadvantage is that to enhance the “kill” rate of bacteria and othermicrobes it is necessary that there be a sufficiently a highconcentration of Ag-ion on the surface which is not achieved through theuse a one-step process; and further when the 1-step method is usedsignificant color is produced as a consequence. This color makes theglass unsuitable for use in electronic devices by altering the display,for example, by making it less clear or altering the colors.

Disclosed herein is a two-step (2-step) method that avoids thedisadvantages of the 1-step method. The 2-step method uses a firstion-exchange bath containing an ion-exchanging alkali metal compoundwhose ions are larger than the alkali metal ions in the article intowhich they will be exchanged (the standard strengthening method onchemical strengthening), followed by ion-exchange using a secondion-exchange bath containing silver, the second silver-containingion-exchange bath being used for a much shorter time than the firstbath. The second ion-exchange bath contains a high concentration of bothsilver ions and an ion-exchanging alkali metal compound whose ions arelarger than the alkali metal ions in the article into which they beexchanged, the silver ion concentration in the second bath being higherthan that used in the in the silver-containing bath of the 1-stepmethod. In the first step, the larger alkali metal ions are exchangedinto the glass to form a glass article having a compressive stress inthe usual manner for a time greater than 3 hours at a temperature in therange of 300-500° C.; for example, by ion-exchange at 420° C. for 5-6hours. In the second step, the higher concentration of silver ions areexchanged into the surface of the glass and replace the alkali metalions in the glass to a shallow enough depth without significant loss ofcompressive stress. In one embodiment of the 2-step method, the samealkali metal compound can be used in both the first and secondion-exchange baths. In certain embodiments of the 2-step method thesilver compound and alkali metal compound used in the ion-exchange bathare both comprised of nitrates. Furthermore, the potassium ions aretypically ion-exchanged for sodium and lithium alkali metal ions in theglass.

Generally, the 2-step method comprises providing a glass articlecontaining ion-exchangeable alkali metal ions, providing a firstion-exchange bath containing ion-exchanging alkali metal compound whoseions are larger than the alkali metal ions in the article, and, as afirst step, ion-exchanging the alkali metal ions in the glass for thealkali metal ions in the ion-exchange bath. As a second step, the methodfurther comprises providing a second ion-exchange bath containing silvernitrate in an amount in the range of 1-10 wt %, the remainder of thebath being the nitrate of the an alkali metal ion having ion larger thanthe alkali metal ions at least equal in size to the alkali metal ions ofthe first ion-exchange bath. In one embodiment, the duration of thesecond bath exposure, that is, the ion-exchange time using the secondbath, is less than 30 minutes in order to produce a shallow depth ofexchange of less than 20 μm. In another embodiment the ion-exchange timeis greater than zero and less than or equal to 20 minutes. In anadditional embodiment, the ion-exchange time is greater than zero andless than or equal to 10 minutes. In all embodiments, the ion-exchangeis carried out at a temperature in the range of 370° C. to 450° C. usinga selected ion exchange time as described herein. In one embodiment, theion exchange is carried out at a temperature in the range of 400° C. to440° C. using a selected ion exchange time as described herein. Thedistinct advantage of the 2-step method is that since only the surfaceconcentration of Ag⁺¹ is important for the antimicrobial effect, havingthe silver penetrate to greater depths as is achieved through the 1-stepmethod adds nothing to the antimicrobial or antibacterial effect sincesilver ions do not move or migrate within the glass at temperatures atwhich electronic devices may be used; temperatures which typically rangefrom below 0° C. to as high as 45° C. or higher. The 2-step method thusallows one to obtain a significantly higher concentration of Ag⁺¹ ionson the surface of the glass which results in a commensurate decrease inthe “kill” time (the time to reach a log 3 reduction) while notproducing any undesirable yellow color and therefore achieving thedesirable transmittance characteristics as is shown in FIG. 1.

FIG. 1 compares the transmission in the 400-750 nm range of anantimicrobial glass ion-exchanged for 20 minutes using the 2-step methodwith an antimicrobial glass prepared by the 1-step method using the sameion-exchange bath for 5 hours. The glass of the 2-step method has atransmission, uncorrected for reflection losses, of greater than 88%over the entire range whereas the glass prepared by the 1-step method isless than 88% in the range of 400 mm to approximately 560 nm and equalto or greater than 88% only in the range of approximately 560 nm to 750nm.

As mentioned above, the 2-step method, by restricting the second step tovery short times, <30 minutes, one can produce a high concentration ofAg⁺¹ on the surface without imparting any color. In fact the silver ionconcentration on the surface is larger for the short IOX time of the2-step method compared to the longer IOX time (typically 4-6 hours) ofthe 1-step method. The volume concentration of Ag ion in the first 5 nmof the glass can be determined using XPS (x-rayphotoluminescence-spectroscopy. Tables 1 and 2 show the XPS results forthe Ag ion concentration in the first 5 nm of the glass.

TABLE 1 1-step Ion-Exchange Sample No Ag concentration, Atomic % 1 1.852 1.55 3 1.86 4 1.94 average 1.80 95% uncertainty 0.28 All samplesion-exchanged using the 1-step method and a 5 wt % AgNO₃/95 wt % KNO₃bath at 420° c. for 5.5 hours

TABLE 2 2-step Ion-Exchange Sample No Ag concentration, Atomic % 1 2.682 1.97 3 2.22 4 3.22 Average 2.52 95% uncertainty 0.90 All samples wereion-exchanged using the 2-step method and a second step 5 wt % AgNO₃/95wt % KNO₃ bath at 420° c. for 20 minutes

A comparison of the Tables 1 and 2 shows that the glass prepared by the2-step method, 20 minute IOX time for the second bath, has a 40%increase in the Ag ion concentration in the first 5 nm relative to theAg ion concentration in the glass produced by the 1-step, single bathprocess, 5% AgNO₃/95% KNO₃ bath being used in both processes.

Another aspect the present disclosure is the ability to produce a glassthat has an antimicrobial surface that is easily cleanable without theloss of the antimicrobial activity. A “low surface energy” coating isapplied to the surface of the silver-containing, chemically strengthenedantimicrobial glass to impart easy-to-clean properties to the glasssurface. The low surface energy coating is a hydrophobic coating thatfacilitates the ease of cleanability of the surface. In one embodiment,the low surface energy coating has a thickness in the range of 0.5 nm to20 nm. In another embodiment, the low surface energy coating is acontinuous coating and has a thickness in the range of 0.5 nm to 10 nm.In a further embodiment, the film is continuous and has a thickness inthe range of 0.5 nm to 5 nm. In an additional embodiment, the thicknessis in the range of 1 nm to 5 m. In an additional embodiment, the film iscontinuous and has a thickness in the range of 1 nm to 5 nm. In anotherembodiment, the low surface energy coating can form a pattern or domainson the surface, for example without limitation, “islands-in-the-sea”where the silver-containing, chemically strengthened surface of theglass is the sea and the low surface energy coating forms the islands.Stated another way, the low surface energy coating is discontinuous anddoes not cover every portion of the glass surface, but does cover asufficient portion of the surface such that the coating is effective forits intended antimicrobial use and for its use in facilitating ease ofcleanability. Such discontinuous coating can also vary in thickness overthe range of 0.5 nm to 20 nm. In one embodiment, the discontinuouscoating has a thickness in the range of 0.5 nm to 10 nm. In anadditional embodiment, the discontinuous coating has a thickness in therange of 1 nm to 5 nm. In a still further embodiment, the coating can bea continuous “peak-to-valley” (“PV”) coating where the coating “peak” isthicker than the coating “valley”. For example, within the range of 0.5nm to 20 nm, the coating within the “peak” can be in the range of 15 nmto 20 nm and the coating within the “valley” areas can be, for example,in the range of 1 nm to 5 nm. The selected depth to which the Ag⁺¹ ionsare deposited may vary according to the silver concentration in the IOXbath, the temperature of the bath and the time for which theion-exchange of the silver ions into the glass was carried out.

In one embodiment, the surface of the glasses described herein havingantimicrobial activity and exhibiting a surface Ag ion concentration ofgreater than zero to 0.05 μgAg/cm², are not cytotoxic. In anotherembodiment, the non-cytotoxic glass has a surface Ag ion concentrationin the range of 0.005 μgAg/cm² to 0.047 μgAg/cm². In an additionembodiment the non-cytotoxic glass has a surface Ag ion concentration inthe range of 0.005 μgAg/cm² to 0.035 μgAg/cm². In a further embodiment,the non-cytotoxic glass exhibits a surface concentration in the range of0.01 μg/cm² to 0.030 μg/cm². In an additional embodiment the surfaceconcentration of the non-cytotoxic glass is in the range of 0.015 μg/cm²to 0.03 μg/cm².

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of the optical transmission (not corrected forreflection losses) comparing the results from the 1-step process (5 wt %AgNO₃ in KNO₃, 5.5 hours, 420° C.) for incorporating Ag ions into aglass with the 2-step process (100 wt % KNO₃, 420° C., 5.5 hours,followed by 5 wt % AgNO₃ in KNO₃, 95 wt % KNO₃, 20 minutes, 420° C.) forAg ion incorporation into a glass.

FIG. 2 is an SEM micrograph of the surface of a chemically strengthened,silver ion containing antimicrobial glass coated with a low surfaceenergy coating, the micrograph showing the domains of the coatingmaterial as dots of varying size on the surface of the glass.

FIG. 3 is a schematic diagram of the modified JISZ 2801: 2000 methodused for evaluating the antibacterial properties of silver-containingglass having a hydrophobic coating on their surface.

FIG. 4 is graph of EMP results showing the actual silver ionconcentration, calculated Ag₂O, versus depth for glass samples that wereprepared by the 2-step method using different concentrations of AgNO₃ inthe second bath.

FIG. 5 is a graph of EPM results illustrating the decrease in Ag ionconcentration as one proceeds from the center of the glass to thesurface of the glass.

FIG. 6A is a graph illustrating Ag ion surface concentration inions/cm²×10¹⁴ versus wt % Ag₂O.

FIG. 6B is a graph of a graph of the Ag surface concentration in μg/cm²versus the wt % Ag₂O.

FIG. 7 is a graph comparing the antimicrobial activity, as log reductionversus time, for a silver ion containing glass as prepared by the 2-stepmethod using a second IOX bath containing 0.15 wt % Ag.

FIG. 8 is a graph of bacterial “kill” time versus surface Ag-ionconcentration.

DETAILED DESCRIPTION

As used herein the term “antimicrobial,” means an agent or material, ora surface containing the agent or material that will kill or inhibit thegrowth of microbes from at least two of families consisting of bacteria,viruses and fungi. The term as used herein does not mean it will kill orinhibit the growth of all species microbes within such families, butthat it will kill or inhibit the growth or one or more species ofmicrobes from such families. The components of all the glasscompositions suitable for ion-exchange are given in terms of weightpercent (wt %) as the oxide unless indicated otherwise. The surfaceconcentration of antimicrobial silver ions is given in μg/cm² and refersto the concentration on the surface of the glass, and not to silver ions“near” or “close to” the surface. Also herein the term “2-step method”includes not only the glass compositions recited herein, but also anyglass composition, from any source, that is suitable for chemicalstrengthening by ion-exchange to impart a compressive stress to theglass, or any glass that may have been chemically strengthened foranother purpose and is used to prepare an antimicrobial glass accordingto the second step of the 2-step method.

As used herein the term “Log “Reduction” or “LR” means Log (Ca/C₀),where C_(a)=the colony form unit (CFU) number of the antimicrobialsurface containing silver ions and C₀=the colony form unit (CFU of thecontrol glass surface that does not contain silver ions. That is:

LR=−Log(C _(a) /C ₀),

As an example, a Log Reduction of 4=99.9% of the bacteria or viruskilled and a Log Reduction of 6=99.999% of bacteria or virus killed.

As used herein the term “low surface energy coatings” are hydrophobiccoatings, for example without limitation,

-   -   (a) (RO)_(4-z)—Si—[(CH₂)₃—OCF₂—CF₂-[OCF₂—CF₂—CF₂]_(n)—F]_(z),        where z=1 or 2, n is an integer sufficient to provide that        [(CH₂)₃—OCF₂—CF₂—[OCF₂—CF₂—CF₂]_(n)—F] has a length in the range        of nm to 20 nm, and RO═CH₃O—, CH₃—CH₂O—, or CH₃C(O)O—, and    -   (b) (RO)_(4-z)—Si—[(CH₂)_(x)—(CF₂)_(y)—CF₃]_(z), where x+y are        integers whose sum is sufficient to provide that        [(CH₂)_(x)—(CF₂)_(y)—CF₃] has a length in the range of 1 nm to        20 nm, with the provision that y≧x, z is 1 or 2, and RO═CH₃O—,        CH₃—CH₂O—, or CH₃C(O)O—.        The values of n, x and y in the above two formulas can be        determined using the covalent radius of carbon and oxygen which        are 0.077 nm and 0.073 nm, respectively. The coating has to have        a sufficiently long spacer, for example, a plurality of —CH₂—,        —CF₂—, —O—(CH₂ and/or CF₂)_(n) moieties, or combination or such        moieties, between the Si atom and the terminal fluorocarbon        group, for example, CF₃, so that water can contact the glass        surface of the glass and transport silver ions from the glass to        a microbe. In one embodiment, the total length of the spacer or        skeletal chain from the silicon atom and the chain's terminal        moiety, for example, CF₃, is in the range of 1-20 nm. In another        embodiment, the total length is in the range of 2-10 nm. In        another embodiment, the total length is in the range of 1-10 nm.        The silane coating material is attached to the silver-containing        glass's surface by 2 or 3 Si—O bonds.

The methods described herein can be used to make antimicrobial glasssamples of any thickness. In one embodiment, for example, for use inelectronic devices as a touch screen or a touch screen cover glass, forexample without limitation, cell phones, computer (including laptops andslates) and ATMs, the glass typically has a thickness in the range of0.2 mm to 3 mm. In one embodiment the glass has a thickness in the rangeof 0.2 mm to 2.0 mm. In a further embodiment, the glass has a thicknessin the range of 0.3 mm to 0.7 mm. The exemplary glass samples describedand used herein for testing were 0.5 mm thick unless specifiedotherwise. Other applications include use as table tops or cover top,shelving in refrigerators or for storage shelves or shelf cover in, forexample, laboratories, hospitals and other facilities whereantimicrobial properties are desired. It should be noted that the glasscan be thicker according to the intended use. For example, for ahospital bench top or bench top cover, it may be desirable that theglass have a thickness of greater than 3 mm.

Any glass composition capable of being ion-exchanged can be used inaccordance with this disclosure. Such glass compositions typicallycontain the smaller alkali metal ions, typically Na and Li ions that canbe exchanged by larger alkali ions, for example by K, Rb and Cs ions andsilver ions. In addition, any glass composition, from any source, thatis suitable for chemical strengthening by ion-exchange to impart acompressive stress to the glass, or that may have been chemicallystrengthened for another purpose, can be used to prepare anantimicrobial glass according to the second step of the 2-step methoddescribed herein.

Glass compositions that can be used in practicing this disclosureinclude, without limitation, soda lime, alkali aluminosilicate andalkali aluminoborosilicate glasses. Examples of glasses that can be usedare disclosed in commonly assigned U.S. Patent Application PublicationNos. 2010/0035038, 2010/0028607, 2010/0009154, 2009/0220761 and2009/0142568, the teaching of which are incorporated herein byreference. Exemplary alkali aluminosilicate glass compositions,particularly the base glass compositions, suitable for ion-exchangeusing an ion-exchange bath including silver ions include:

-   -   (a) 60-70 mol % SiO₂; 6-14 mol % Al₂O₃; 0-15 mol % B₂O₃; 0-20        mol % Na₂O; 0-10 mol % K₂O; 0-8 mol % MgO; 0-10 mol % CaO; 0-5        mol % ZrO₂; 0-1 mol % SnO₂; 0-1 mol % CeO₂; less than 50 ppm        As₂O₃; and less than 50 ppm Sb₂O₃; wherein 12 mol %≦Na₂O+K₂O≦20        mol % and 0 mol %≦MgO+CaO≦10 mol %.    -   (b) 64 mol %≦SiO₂≦68 mol %; 12 mol %≦Na₂O≦16 mol %; 8 mol        %≦Al₂O₃≦12 mol %; 0 mol %≦B₂O₃≦3 mol %; 2 mol %≦K₂O≦5 mol %; 4        mol %≦MgO 6 mol %; and 0 mol %≦CaO≦5 mol %, and wherein 66 mol        %≦SiO₂+B₂O₃+CaO≦69 mol %; Na₂O+K₂O+B₂O₃+MgO+CaO+SrO>10 mol %; 5        mol %≦MgO+CaO+SrO≦8 mol %; (Na₂O+B₂O₃)−Al₂O₃≦2 mol %; 2 mol        %≦Na₂O−Al₂O₃≦6 mol %; and 4 mol %≦(Na₂O+K₂O)−Al₂O₃≦10 mol %;    -   (c) 61 mol %≦SiO₂≦75 mol %; 9 mol %≦Na₂O≦21 mol %; 7 mol        %≦Al₂O₃≦15 mol %; 0 mol %≦B₂O₃≦12 mol %; 0 mol %≦K₂O≦4 mol %; 0        mol %≦MgO≦7 mol %; and 0 mol %≦CaO≦mol %;    -   (d) 50 mol %≦SiO₂≦70 mol %; 8 mol %≦Na₂O≦16 mol %; 9 mol        %≦Al₂O₃≦17 mol %; 2 mol %≦B₂O₃≦12 mol %; 0 mol %≦K₂O≦4 mol %; 0        mol %≦MgO≦4 mol %; and 0 mol %≦CaO≦0.2 mol %. wherein the alkali        metal oxides and the alkaline earth metal oxides are modifiers        and the ratio [(mol %≦Al₂O₃+mol % B₂O₃)÷Σ mol %≦modifiers] is        greater than 1, that is:

[(mol % Al₂O₃+B₂O₃)÷Σmol %≦modifiers]>1; and

-   -   (e) SiO₂>50 mol %; 11 mol %≦Na₂O≦25 mol %; 7 mol %≦Al₂O₃≦26 mol        %; 0 mol %≦B₂O₃≦9 mol %; 0 mol %≦K₂O≦2.5 mol %; 0 mol %≦MgO≦8.5        mol %; and 0 mol %≦CaO≦1.52 mol %.        The alkali aluminosilicate glass and alkali-aluminoborosilicate        glasses are substantially free of lithium, meaning any lithium        present is as a contaminant, whereas in other embodiments, the        alkali aluminosilicate glass is substantially free of at least        one of arsenic, antimony, and barium. In other embodiments, the        alkali aluminosilicate glass has a liquidus viscosity of at        least 130 kilopoise and is down-drawable by those techniques        known in the art, for example, but not limited to, fusion-draw        processes, slot-draw processes, and re-draw processes. In        another embodiment the glass can be made by the float process.

A further example, without limitation, of an alkali aluminosilicateglass that can be used in the present disclosure is one described in thecommonly assigned U.S. Patent Application Publication No. 2010/0009154as having a composition of: 66 mol % SiO₂; 14 mol % Na₂O; 10 mol %Al₂O₃; 0.6 mol % B₂O₃; 2.5 mol % K₂O; 5.7 mol % MgO; and 0.6 mol % CaO;0.2 mol % SnO₂; and 0.02 mol % ZrO₂. The sodium in this glass, and otherexemplary glasses, can be exchanged with, in addition to silver ions,potassium, rubidium, or cesium to produce a region of high compressivestress near the surface and a region under central tension in theinterior or central region of a glass part. Unless otherwise specified,it is understood that use of the terms “lithium,” “sodium,” “potassium,”“cesium,” and “rubidium” herein refers to the respective monovalentcations of these alkali metals. If rubidium and cesium are used in theion-exchange bath they can then also be exchanged for potassium ions aswell as for sodium and/or lithium ions in the glass. In one embodiment,some or all of the sodium and/or potassium in the glass compositionas-made can be replaced are replaced by lithium in the glass. Thelithium can then be ion-exchanged with silver, sodium, potassium,rubidium, or cesium to obtain a high surface compressive stress and aninterior volume under tension. In order to produce surface compressivestress (as opposed to tension), one or more of the ions in the glassmust be replaced by an ion in the salt solution that has a higher atomicnumber; for example, silver and sodium replace lithium in the glass, andsilver and potassium replace sodium and/or lithium in the glass.

In the examples of the present disclosure, the chemical strengthening ofglasses used as an exemplary cover glass article was accomplished in thefirst step of the disclosed 2-step ion-exchange process where a largerion such as K⁺¹ (from KNO₃) is exchanged for a smaller ions in theglass, for example Na⁺¹ or Li⁺¹. The base glass, before anyion-exchange, used to prepare the antimicrobial glass sample articlesevaluated herein has a composition, in weight percent, falling withinthe range of 66±2 wt % SiO₂, 13±1.5 wt % Al₂O₃, 13±3 wt % Na₂O, 1.5±0.5wt % K₂O, 4±1 wt % MgO, 0.5±0.2 wt % CaO, less than 1 wt % SnO₂, lessthan 0.8 wt % ZrO₂ and less than 0.5 wt % Fe₂O₃; and the analyzedspecific composition of the base glass actually used to prepare thesamples was 66.02 wt % SiO₂, 13.6 wt % Al₂O₃, 13.7 wt % Na₂O, 1.7 wt %K₂O, 3.9 wt % MgO, 0.45 wt % CaO,). 44 wt % SnO₂, 0.04 wt % ZrO₂ and0.017 wt % Fe₂O₃, This first step can also be accomplished independentlyby the use of a glass that has already been chemically strengthened byion-exchange, even though such strengthening was carried out for adifferent purpose, for example, simply providing a chemicallystrengthened, but not antimicrobial, glass. Thus, the first step of the2-step method described herein can be accomplished by either means. Inthe second step of the 2-step method described herein silver ions areexchanged into the glass using a bath containing both silver andpotassium ions, present as for example nitrates, where the AgNO₃concentration can be in the range 0.1-10 wt % and the ion-exchange iscarried out for a time in the range of 1 minute to less then 30 minutesat a temperature in the range of 370° C. to 450° C.

In the examples described herein, KNO₃ was used as the alkali metal inthe ion-exchanging salt baths and AgNO₃ was used as the source of silverion. For all the examples, unless specified otherwise, the ion-exchangeswere carried out at 420° C. for the time indicated for sample asdescribed herein.

Method of Quantifying the Surface Ag⁺¹ Concentration

The antibacterial action produced by the silver ions is a “surfaceeffect.” In other words, what is important is the nature and extent ofthe contact of the microbe with the silver-containing surface of theglass. Therefore a quantitative knowledge of the surface Ag⁺¹concentration, in μg/cm² or ions/cm², is crucial in ascertaining theeffectiveness of the antimicrobial action. This is even more pertinentin the present case where the Ag is being added by an ion-exchangeprocess. The analytical techniques of EMP (electron microprobe) and XPS(X-ray photoluminescence spectroscopy) and SIMS (secondary ion massspectroscopy) can be used to obtain the Ag⁺¹ profile, but they yieldvolume concentration values, albeit close to the surface, whereas whatis important is the surface ion concentration. EMP and XPS canquantitatively determine the Ag⁺ concentration to within 10-20 nm.TOF-SIMS (time-of-flight secondary ion mass spectroscopy) can looknearer to the surface but it is non-quantitative. What makes theestimate of the surface concentration more difficult is that the Ag⁺¹concentration actually decreases as one nears the surface as shown fromthe EMP measurements of FIG. 4. FIG. 4 is graph of EMP results showingthe actual silver ion concentration, calculated Ag₂O, versus depth forglass samples that were prepared by the 2-step method using differentconcentrations of AgNO₃ in the second bath, where the first IOX bath was100 wt % KNO₃ and the second IOX baths were KNO₃ baths containing 1 wt %(♦), 2 wt % (▪) or 5 wt % (▴) AgNO₃, respectively, and the second bathion-exchange time and temperature were 20 minutes and 420° C.,respectively.

The following Table 3 gives the Ag ion bath concentrations, the time forion-exchange and the resulting EMP measurements, as wt % Ag₂O, forseveral different ion-exchanges. Except for the sample ion-exchanged for300 minutes, the samples in Table 3 were prepared using the 2-stepmethod. The sample having an ion-exchange time of 300 minutes wasprepared by the 1-step method using the same ion-exchange bath havingthe same composition as the second bath of the 2-step process. All theglass articles of Table 3 have a compressive stress of at least 250 MPa.In one embodiment the compressive stress is at least 500 MPa. In anotherembodiment the compressive stress is at least 600 MPa. The number term“EMP (15 nm)” refers to a depth which is close as close as theaccelerating potential of the method allows. All ion-exchanges of Table3 were carried out at 420° for both the 1-step sample and the 2-stepsamples. In the 2-step process the first ion-exchange was done usingKNO₃ only for a time of 5.5 hours, and the second ion-exchange was doneusing an AgNO₃/KNO₃ bath. The Ag/K bath compositions are given in Table3.

TABLE 3 Ag wt % in bath IOX time, minutes EMP (≅15 nm), wt % 0.15* 200.82 0.15‡ 330 (5.5 hours) 1.0 0.25* 20 1.0 0.5* 20 2.2 1.0* 20 5-7 2.0*20 7.1-8.1 5.0* 20 12.3-15.3 10.0* 10 23-25 Wt % was calculated as theoxide, Ag₂O *= made using the 2-step process ‡= made using the 1-stepprocess

The EMP method used was to vary the accelerating potential to accessdifferent depths in the glass samples. The glasses of FIG. 5 are themeasured values of the wt % Ag₂O vs. depth as a function of the AgNO₃bath concentration in the 2^(nd) step of the 2-step process describedabove.

XPS (x-ray photoluminescence spectroscopy), was also used to estimatethe Ag concentration. Although XPS is usually referred to as a surfacemeasurement, it actually measures to a depth 5-10 nm, with approximately95% of the signal coming from ≦5 nm of the surface. Therefore XPS datashould also be interpreted in a way similar to that used to interpretthe EMP while data recognizing that the XPS data is from an area closerto the surface of the glass. The XPS results are reported as an atomicpercent of the atoms on the surface of the glass substrate and are shownin Table 4. Table 4 also includes the EMP results for the same samplesthat were XPS analyzed. In Table 4 the samples showing an ion-exchangetime of 5.5 hours were prepared using the 1-step method. The samplehaving an ion-exchange time of 20 minutes was prepared using the 2-stepmethod AG IOX was carried out in the second step.

TABLE 4 Comparison of Ag concentration from XPS and EMP estimates Ag IOXAg⁺¹ Wt % in Time at At % Ag₂O Wt % Ag₂O Wt % Bath 420° C. XPS XPS(calc) EMP N/cm³ 0.1‡ 5.5 hours 0.98 2 2   2 × 10²⁰ 5%*  20 minutes 9.219 19 2.28 × 10²¹ 5%‡ 5.5 hours 12.6 26 24 3.00 × 10²¹ *= 2-step method‡= 1-step method

The agreement in the amount of Ag₂O is excellent, thus indicating thatboth methods are measuring the same volume concentration.

While the data presented above provides estimates of the volumeconcentration, the following paragraphs describe how to determine theactual surface concentration since this is the relevant numberpertaining to antimicrobial behavior. Silver in the body of the glassbelow the surface plays no antimicrobial role since it has no access tothe bacteria on the surface.

Determination of the surface concentration can also be done using astatistical method. The relationship is simply derived from the idea ofan array of particles N along a line defined as N/cm. Extending thisarray this to a plane gives one surface concentration N²/cm², andsimilarly extending it to a cube provides a volume concentration N³/cm³.The fact that the array is disordered is not a limitation as long as onecan define an average. In other words, an isotropic homogeneous array ofparticles allows an average number of particles per unit dimension to bedefined. This approach allows one to define the relationship between thesurface concentration and the volume concentration as shown in thefollowing Equation 1.

N/cm²=[N/cm³]^(2/3)  Eq. 1.

Using the EMP volume concentration estimates for various IOX schedules,one can make the graphs shown in FIGS. 6A and 6B. FIG. 6A, is a graph ofthe Ag-ion surface concentration in ions/cm²×10¹⁴ versus the Ag₂Oconcentration in wt %. One can also calculate the values of the surfaceconcentration in μg/cm². The conversion of the estimates of surfaceconcentration given above to units of μg/cm² allows comparison to someof the literature.

For the estimate from equation 1, one must use the N/cm² to convert toμg/cm² as shown in Equation 2.

$\begin{matrix}{\frac{\mu g}{{cm}^{2}} = {{\frac{N}{{cm}^{2}}\frac{1}{2}{MW}\; {Ag}} = {\left( {N/{cm}^{2}} \right)\left( {1.8 \times 10^{- 22}} \right)}}} & {{Eq}.\mspace{14mu} 2}\end{matrix}$

FIG. 6B, is the surface concentration expressed in μg/cm² vs. wt % Ag₂Oin the glass

The 2-step method permits much higher Ag⁺¹ surface concentration to beachieved without any other undesirable effects. The very important andunique advantage of the higher surface concentration is the decrease inthe bacteria “kill” time. This is the time that is required to produce asignificant log reduction ≧2 as described below. FIG. 8 shows thedependence of the “kill” time as a function of the surface concentrationusing samples prepared by the 2-step method to have varying surfaceconcentrations which were determined as described herein. The value ofthe “kill” time is a significant feature of the intended applicationsfor all uses including hand-held device applications. It is only byusing the 2-step method can one produce “kill” times of any practicalutility as will be shown below, particularly for electronic devicescolored cover or touch screen would impair the user's visual experience.

It was further noted that the silver ion concentration increases as onegoes further into the glass from the surface. While the origin of thisphenomenon is uncertain, it was verified as real by a comparison ofbacterial Log Reduction values as shown in FIG. 7 for a silver ionexchanged glass. FIG. 7 is a graph comparing the antimicrobial activity,as log reduction versus time, for a silver ion containing glass asprepared by the 2-step method using a second IOX bath containing 0.15 wt% Ag. Sample A (diamond ♦) represents the antimicrobial glass asprepared using the (0.15 wt % Ag bath, and Sample A-R (square ▪)represents the same glass after the removal of 1 μm of the glasssurface. The data of FIG. 7 indicate that the while Samples A and A-Rhave achieve substantially the same Log Reduction value during theduring first approximately 100 minutes, after approximately 250 minutesthe A-R Sample, which had the top 1 μm of glass removed, exhibited amuch higher Log Reduction value. This illustrates that the Ag contentactually increases as the distance from the surface increases and theimportance of having as high a surface concentration as possible tomaximize antimicrobial activity.

Antimicrobial Testing

Antibacterial tests were carried out using cultured gram negative E.coli; DH5alpha-Invitrogen Catalog No. 18258012, Lot No. 7672225,rendered Kanamycin resistant through a transformation with PucI9(Invitogen) plasmid). The bacteria culture was started using either LBKan Broth (Teknova #L8145) or Typtic Soy Broth (Teknova # T1550).Approximately 2 μl of liquid bacteria suspension or a pipette tip fullof bacteria were streaked from an agar plate and dispensed into a cappedtube containing 2-3 ml of broth and incubated overnight at 37° C. in ashaking incubator. The next day the bacteria culture was removed fromthe incubator and washed twice with PBS. The optical density (OD) wasmeasured and the cell culture was diluted to a final bacterialconcentration of approximately 1×10⁶ CFU/ml. The cells were placed onthe selected glass surface, antimicrobial or not antimicrobial (thecontrol) for 6 hours at a temperature of 37° C. The buffers from eachwell were collected and the plates were twice washed with ice-cold PBS.For each well the buffer and wash were combined and the surfacespread-plate method was used for colony counting.

Antimicrobial properties were exhibited in glass samples prepared using1-step and 2-step methods. The control sample in all cases is anion-exchanged glass that does not contain silver. Each of the glasssamples was cut into a glass slide of 1×1 square inch (2.54 cm×2.54 cmsquare) and placed in a Petri dish. Three glass slides were used asnegative controls. Gram negative E. coli bacteria were suspended in a1/500 LB medium at a concentration of 1×10⁶ cells/ml. 156 μl of E. colicell suspension was placed onto each sample surface and held in closecontact by using a sterilized laboratory PARAFILM®, and incubated for 6hours at 37° C. at saturation humidity (>95% relative humidity). Eachsample was produced in triplicate. After 6 hours incubation, 2 ml of PBSbuffer was added into each Petri dish. After shaking, both the slide andPARAFILM® were washed, and all the solution from each Petri dish wascollected and placed onto a LB agar plate. After further 16-24 hourincubation at 37° C., the bacteria colony formation on the agar platewas examined. The results are shown by the bacterial growth response:Log reduction=−Log(C_(a)/C₀), where C_(a) is the concentration ofbacteria (or virus or fungus) after exposure to the antimicrobialsurface and C₀ is the concentration of bacteria of the control sample inwhich the bacteria is not in contact with an antimicrobial surface. Asan example, a Log Reduction of 3=99.9% of bacterial or virus killed anda Log Reduction of 5=99.999% of bacteria or virus killed. The followingTable 5 shows log reduction vs. surface Ag concentration.

For the purposes of the test and to insure that no bacterialcontamination was initially present on the glass before the testingbegan, all the ion-exchanged glass samples, with or without silver, weresterilized by washing with 70 Vol. % ethanol for 1 minutes and wipedusing distilled water. Table 5 show the results of bacterial testingresults of glass samples after 6 hours using antimicrobial glass havingsurface silver ion concentrations, calculated as Ag₂O, as described inTable 5. The glasses in Table 5 were all prepared by the 2-step method.The first step IOX was carried out using a 100 wt % KNO₃ bath for a timein the range of 5-6 hours at a temperature of approximate 420°. Thesecond step IOX was carried out using The surface Ag⁺¹ concentration,calculated in μg/cm², was determined as described herein

TABLE 5 Bacterial test: 2-Step Antimicrobial Glass Showing LR >5 After 6Hours Sample, Ag⁺¹, μg/cm² 2^(nd) Step IOX Conditions Log Reduction0.0155 420° C., 5 minutes >5 0.0155 420° C., 10 minutes >5 0.016 420°C., 20 minutes >5 0.03 420° C., 5 minutes >5 0.0325 420° C., 10minutes >5 0.036 420° C., 20 minutes >5

Table 6 Illustrates that the rate of bacterial reduction is faster forsamples prepared using the 2-step method when compared to the 1-stepmethod.

TABLE 6 Bacterial Test Results Time, minutes 1-Step Method 2-Step Method0 0 0 45 0.23 0.34 90 2.95 3.7 180 >5 >5 270 >5 >5 360 >5 >5

Antiviral Test

An antiviral test was carried out using an Ag ion-exchanged glass havinga surface ion concentration of 0.03 μg/cm² and HIV as the test virus. ALog Reduction of 2.22 was obtained after 1 hour.

Cytotoxicity Test

Cytotoxicity studies were conducted using NIH3T3 mouse fibroblast cellsfor culturing. Glass slides, 1×1 square inch (25.4 mm×25.4 mm), wereattached to the bottom of a 96-well Holey plate. For the purposes of thetest and to insure that no bacterial contamination was initially presenton the glass before the cytotoxicity testing began, all theion-exchanged glass samples, with or without silver, were sterilized byirradiation with UV light for 10-30 minutes, soaked in 70 Vol. % for 15minutes and then wiped using distilled water. Four wells were culturedfor each glass slide. The seeding density of each well was approximately2×10⁴ cells per well. After seeded wells were incubated for three daysat 37° C. they were visually inspected using a live/dead stain and afluorescence microscope for the counting of dead cells or colonies. Nodead cells were observed for Samples C1, C2, C3 and C4 (Table 7).

TABLE 7 Sample Ag μg/cm² Cytotoxicity C0 0 0 = No cytotoxicity observedC1 0.015 0 C2 0.005 0 C3 0.065 0 C4 0.08 0 C0 = Control, IOXedaluminosilicate glass, No Ag C1-C4 = prepared by the 2-step process asindicated; in μg/cm²

For use in hospitals and laboratories where mammalian cells infectedwith bacteria, viruses or fungi may be present, and coloring of theglass is not a consideration, higher concentrations of silver ions canbe attained using the methods described herein.

Coatings

Another important aspect of the disclosure are the methods by which theantimicrobial behavior is maintained when selected functional coatings(including films) are placed on the surface of the antimicrobial,chemically strengthened glass. For example, in many touch screenapplications (phones, computers, ATMs, etc) where the glass is used as acover glass, a coating or film is placed on the glass surface so thatfingerprints can be cleaned relatively easily. The coating(s) thatfacilitate cleaning are low surface energy coatings, for example,coatings in the class of “fluoroalkylsilanes” of general formulaA_(x)-Si—B_(4-x), where A is selected from the group consisting ofperfluoroalkyl R_(F)—, perfluoroalkyl terminated perfluoropolyether,perfluoroalkyl-alkyl, copolymers of fluoroalkene silanes and alkenesilanes, and mixtures of fluoroalkylsilanes and hydrophilic silanes, Bis Cl, acetoxy [CH₃—C(O)—O-] or alkoxy [for example CH₃O— or C₂H_(S)O-],and x=1 or 2. Low surface energy coatings of the foregoing types arecommercially available from different manufacturers, for example, DowCorning, [DC2634-a perfluoropolyether silane in which the functionalperfluoro moiety is Poly[oxy(1,1,2,2,3,3-hexafluoro-1,3-propanediyl)],α-(heptafluoropropyl)-ω-[1,1,2,2-tetrafluoro-3-(2-propenyloxyl)propoxy];Gelest [SIT8174.0, Tridecafluorotetrahydrooctyltrichlorosilane;SIT8371.0, Trifluoropropyltrichlorosilane; SIH5841.0Heptadecafluorotetrahydrodecyl trichlorosilane; and SIH5841.0(heptadecafluoro-1,1,2,2-tetrahydrodecyl)trichlorosilane;

SIH5841.5 (heptadecafluoro-1,1,2,2-tetrahydrodecyl)trimethoxysilane; andSIH5841.2 (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane];Cytonix [FSM 1200 Perfluoropolyether mono-silane; FSD 2500 Mediummolecular weight perfluoropolyether di-silane; FSD 4500 High molecularweight perfluoropolyether polysilanes]. The low surface energy coatingshould have a spacer or skeletal chain length in the range of 1 nm-20nm, the skeletal chain being carbon atoms or a mixture of carbon andoxygen atoms in the case of the perfluoropolyethers. In one embodimentthe chain length is in the range of 2 nm to 20 nm. In a furtherembodiment the chain length is in the range of 1-10 nm. Other examplesare

-   -   (a) copolymers of fluoroalkene silanes and alkene silanes; and    -   (b) mixtures of fluoroalkylsilanes and hydrophilic silanes.        Silanes other than the foregoing can also be used provided that        they do not prevent water vapor from reaching the surface of the        glass so that silver ions can be transported from the glass        surface to the microbe to thereby kill the microbe or inhibit        its growth.

Generally, the fluoro-containing coatings describe above have 1 or 2fluorocarbon-containing moieties attached to the silicon and each of themoieties, independently, have a chain length in the range of 1 nm to 20nm, and the chain may include oxygen atoms or sulphur atoms along thechain. In one embodiment the chain length is in the range of 2 nm to 20nm. In a further embodiment the chain length is in the range of 1-10 nm.What is important for the coating is that at least part the fluorocarbonmoiety be sufficiently distant from the surface so that water moleculescan come into contact with the surface, pick up silver ions on thesurface, and transport the silver ions to a microbe where they can beabsorbed in to microbe and thus kill it or decrease its reproductiverate. Consequently, it is preferred that one or two fluorocarbonmoieties be attached to the silicon atom and that the silicon atom bebonded to the glass by two or three Si—O bonds. For example, if thealkyl group of (a) above, which functions as a spacer or skeletal chainbetween the silver-containing glass surface and the fluorocarbon moiety,is too short, then hydrophobic fluorocarbon moiety can block watermolecules from reaching the glass surface and thus silver ions cannot betransported from the surface to and into the microbe. In anotherinstance, without being held to any particular theory, it is believedthat the oxygen atoms in a perfluoropolyether alkoxy silane that hasbeen bonded to the surface of the antimicrobial glass can facilitate themigration of water molecules by oxygen atoms along the chain to thesurface where the water molecules can coordinate to silver ions andfacilitate the ions transport to the microbe. An exemplaryperfluoropolyether alkoxy silane is Dow Corning® 2634 used as 0.02-1 wt% solutions in a fluorinated solvent. After the coating material wasapplied to the antimicrobial glass article such as described herein, thecoating was cured to adhere the coating to the surface of the glassarticle and finally sonicated in a fluorinated solvent (for example,Novec™ HFE7200, 3M Company) bath for a 3 minutes remove any unreactedcoating material. The curing was done thermally by either heating thecoated in an oven, for example, at 50° C., 50% RH, for a cure time assuggested by the manufacturer or by infrared heating of the coatedarticles. The coated article was then heated in an oven for a time inthe range of 30 minutes to 2 hours to cure the coating material to theglass surface.

The method and process for the deposition of these coatings is capableof controlling the thickness and morphology of the coating on thesurface of the glass. Process methods and steps can be introduced wherethe coating was deposited in such a fashion either to be discontinuousor quasi-discontinuous. Such process methods include, but are notlimited to, vapor deposition or spray coating through a predeterminedcoverage mask, ink jet printing, micro contact printing using a masterwhich would allow the fluorosilane to be coated in specific regions,humidity curing to allow phase separation of the fluorosilane. When thecoating is sufficiently thin it can be continuous. Thin continuouscoatings can be deposited, for example, by dip, spray and vapordeposition followed by curing to adhere the silanes, and followed byultrasound cleaning to remove un-reacted but physically adsorbedsilanes. The foregoing procedures allow the antimicrobial action topersist in open uncoated areas, or in areas where the coating is verythin or the surface is coating-free while at the same time maintainingintended functional performance of the coating. FIG. 2 is an AFM (atomicforce micrograph) illustrating this desired morphology in the form oflocalized domains (islands-in-the-sea) of fluorosilane deposited on thesurface of a silver ion containing, chemically strengthened glass asdescribed herein. In FIG. 2 the glass (or sea) is the black backgroundand the coating domains or islands 100 are shown as the white to graydots or ovals of various sizes that are dispersed on the background. Inthe case where the coating is continuous, the coating is relativelythin, having a thickness, in one embodiment, in the range of 0.5 nm to20 nm in order for the antimicrobial activity of the glass surface toremain effective. In another embodiment the thickness of the coating isin the range of 0.5 nm to 5 nm. In a further embodiment the thickness ofthe coating is in the range of 1 nm to 3 nm. In the thin coating case amixed self-assembled monolayer can be prepared on the surface using twosilanes, where one silane is a fluoroalkylsilane and the other silane isa hydrophilic silane (for example, a polyethylene glycol containingsilane), wherein the hydrophilic or “water loving” silane domains assistin the antimicrobial action by capturing water molecules and presentingthem to the surface where the water can pick up silver ions fortransport to the microbe. In one embodiment fluoro-oligoethylene glycolsilanes can also be used, where the oligoethylene glycol part of thesilanes can assist in capturing free water at the interface.

The test method used for determining antibacterial properties of asilver-containing glass having a hydrophobic coating thereon was amodified version of the JISZ-2801: 2000 method, which is a JapaneseIndustrial Standard that was developed to measure the antibacterialactivity of hydrophobic materials, particularly polymers into whichsilver ions had been incorporated. The antibacterial activity ismeasured by quantitatively by determining the survival of bacteria cellsthat have been held in intimate contact with a surface thought to beantibacterial and incubated for 24 hours at 35° C. After the time periodhas elapsed the cells are counted and compared to a non-treated surface.The test was modified in that for the incubation period was changed to 6hours at 37° C. After 6 hours the samples were removed from theincubator and the entire testing surface was thoroughly washed with PBSto ensure that all bacteria were removed. The cells and the PBS washwere then transferred to a broth agar plate for overnight culture. Aftera period of 16-24 hours the bacterial colonies on the agar plate werecounted. FIG. 3 is a diagram illustrating the modified method that wasused. In FIG. 3 numeral 10 represents the addition of a 400 μl bacterialsuspension of concentration 1×10⁶ cells/ml to the sample plates 12 whichcan be either a Ag-containing glass plate or a control (no Ag) plate,covering 14 the plates having a bacterial suspension thereon with thePARAFILM® resulting in PARAFILM® covered plates 16, and thereafterincubating the bacteria at 37° C. for 6 hours as indicated by 18, andlastly counting the colonies as represented by 20. The samples weretested using E. coli (gram negative) bacteria.

Table 8 presents E. coli antibacterial results obtained using 2-step Agion exchanged glass with varying surface concentrations followed by adeposition of the coating. The Control Sample was ion-exchanged using a100% KNO₃ bath (no AgNO₃). The coating material was a fluorosilane whichwas applied to a thickness in the range of 0.5 nm to 5 nm and wasuniform across the surface of the glass. After coating the samples werecured to adhere the silane to the surface of the glass article andfinally sonicated in a fluorinated solvent bath to remove unreactedsilanes.

TABLE 8 Sample IOX Bath % reduction Time, hours S10-NC Control, 100%KNO₃ 0 NA S10-C Control, 100% KNO₃ 0 NA S12-NC 0.015 ug/cm2 99.9 ≧3S13-C 0.015 ug/cm2 99.9 ≧3 S14-NC 0.033 ug/cm2 99.9 ≦2 S14-C 0.033ug/cm2 99.9 ≦2 S10 is the control sample. NC = no coating C = coatedBacterial suspension was E. coli prepared as previously described.Coating was a hydrophobic coating material of less than 20 nm thickness.The tests were repeated twice from the start and produced the sameresults.

There is minimal impact on the compressive stress using the 2-stepmethod, because the depth of the Ag ion exchange into the glass in thesecond step is so shallow, the compressive stress of the glass, whichwas chemically strengthened in a first step by ion-exchange of largerions, typically potassium or larger alkali metal ions, for smaller ionsin the glass as prepared, typically sodium and lithium ions, thecompressive stress of the glass is not measurably affected. Further, itis noted that the ionic radius of silver and potassium ions aresubstantially the same, the Pauling ionic radii of silver and potassiumbeing 1.26 and 1.33 Angstroms, respectively. Consequently, anion-exchange of silver ions for potassium ions already in the glassafter the first step ion-exchange will have a minimal effect on thecompressive stress of the glass. Table 9 compares the compressive stressof the glass samples after the first the first ion-exchange step, KNO₃exchange only, and after the second ion-exchange step using a bathcontaining both AgNO₃ and KNO₃. The samples were tested using theRing-on-Ring test both before and after abrasion. The values in Tableare the average of 3-4 sample tests and the standard deviation is given.Samples were prepared using the 2-step ion-exchange method describedherein. The first step ion-exchange was carried out for 5.5 hours usinga 100% KNO₃ bath at 420° C. A plurality of samples was set aside afterthe first ion-exchange step was completed. The remainder of the sampleswere then subjected to the second ion-exchange step for 20 minutes usinga 5 wt % AgNO₃/95 wt % KNO₃ at 420°

TABLE 9 Before After Step 1 Step 2 Abrasion SD Abrasion SD Sample KNO₃AgNO₃/KNO₃ MPa MPa MPa MPa 1 Yes No 970  ±90 2 Yes Yes 800 ±260 — — 1AYes No — — 380 ±40 2A Yes Yes — — 400 ±40 Samples 1 and 2 results aresamples as-made and before abrasion. Samples 1A and 2A results are forsamples after abrasion. SD = Standard DeviationThe results shown in Table 9 indicate that the second ion-exchange stepwith the AgNO₃/KNO₃ has a minimal effect on the compressive stress.

In an additional embodiment the disclosure is to a method of making anantimicrobial, chemically strengthened glass article, said methodcomprising providing glass article having a first surface, a secondsurface and a selected thickness between said surfaces, and alkali metalions in the glass; providing a first ion-exchange bath consisting of atleast one alkali metal ion larger that the alkali metal ions in theprovided glass to impart a compressive stress greater than 500 MPa intothe glass; providing a second ion-exchange bath consisting essentiallyof 0.005 wt % to 5.0 wt % silver nitrate, the remainder of the bathconsisting of the at least one of the alkali metal ions in the firstbath; ion-exchanging with the second bath to thereby incorporate saidsilver and said alkali metal ion(s) into at least one of said surfacesto form a glass article having a compressive stress of greater than 250MPa and at least one an antimicrobial, chemically strengthened surface;and the concentration of silver ion on the surface of the glass is inthe range of greater than zero to less than 0.047 μg/cm².

Thus, in one embodiment the disclosure is to an antimicrobial,chemically strengthened glass comprising a glass article having acompressive stress layer extending from the surface of the glass to aselected depth in the glass; an antimicrobial Ag+ region that is part ofthe compressive stress layer of the glass article; wherein thecompressive stress in the glass is at least 250 MPa and the surfaceconcentration of the Ag⁺¹ ion is in the range of greater than zero toless than or equal to 0.047 μg/cm². The glass further comprises a lowsurface energy coating on the surface of the glass having thecharacteristic of allowing water molecules to reach the Ag+ ions in theglass. The glass is capable of inhibiting at least 2 microbes species toa Log Reduction greater that 1 within 1 hour. In an embodiment the glasshas an antibacterial Log Reduction of greater than 4 after 6 hours. Inanother embodiment the glass has an antibacterial Log Reduction ofgreater than 5 after 6 hours. In a further embodiment the glass has anAg⁺¹ ion surface concentration in the range of 0.005 μg/cm² to 0.035μg/cm² and is non-cytotoxic. In an additional embodiment the glass hasan Ag⁺¹ ion surface concentration in the range of 0.01 μg/cm² μg/cm² to0.035 μg/cm² and is non-cytotoxic. In an embodiment the glass has anAg⁺¹ ion surface concentration in the range of 0.015 μg/cm² μg/cm² to0.030 μg/cm² and is non-cytotoxic. In another embodiment the compressivestress is at least 500 MPa. In an additional embodiment the compressivestress is at least 600 MPa. The low surface energy functional coatinghas a terminal perfluorinated moiety and is selected from the groupconsisting of silanes of general formula A_(x)-Si—B_(4-x), where A isperfluoroalkyl R_(F)—, perfluoroalkyl terminated perfluoropolyether,perfluoroalkyl-alkyl, copolymers of fluoroalkene silanes and alkenesilanes, and mixtures of fluoroalkylsilanes and hydrophilic silanes, Bis Cl, acetoxy [CH₃—C(O)—O-] or alkoxy, and x=1 or 2; and the coatinghas thickness in the range of 0.5 nm to 20 nm and is bonded to thesurface of the glass by at least one SiO bond between the coatingsilicon atom and an glass oxygen atom. The coating has a skeletal chainlength from the silicon atom to its end, for example, a final CF₃moiety, that is in the range of 2 nm to 20 nm, the skeletal chainconsisting of at least one selected from the group consisting of (a)carbon atoms and (b) a combination of carbon and oxygen atoms in thecase of polyethers. In an embodiment the coating is a perfluoroalkylalkoxy silane of formula (R_(F1))_(x)—Si(OR)_(4-x), where x=1 or 2,R_(F1) moiety is a perfluoroalkyl group having a carbon chain length inthe range of 2 nm to 20 nm and OR is acetoxy, —OCH₃ or OCH₂H₃. Inanother embodiment the coating is(RO)_(4-z)—Si—[(CH₂)₃—OCF₂—CF₂OCF₂—CF₂—CF₂]_(n)—F]_(z), where z=1 or 2,n is an integer sufficient to provide that[(CH₂)₃—OCF₂—CF₂—[OCF₂—CF₂—CF₂]_(n)—F] has a chain length in the rangeof 2 nm to 20 nm, and RO═CH₃O—, CH₃—CH₂O—, or CH₃C(O)O—. In a furtherembodiment the coating is a perfluoroalkyl alkyl alkoxy silane offormula RO)_(4z)—Si—[(CH₂)_(x)—(CF₂)_(y)CF₃]_(z), where x+y are integerswhose sum is sufficient to provide that [(CH₂)_(x)—(CF₂)_(y)—CF₃] has alength in the range of 2 nm to 20 nm, with the provision that y≧x, z is1 or 2, and RO═CH₃O—, CH₃—CH₂O—, or CH₃C(O)O—.

In an embodiment the antimicrobial, chemically strengthened glass isselected from the group consisting of an antimicrobial, chemicallystrengthened alkali aluminosilicate glass and an alkalialuminoborosilicate glass, and the glass has a silver ion surfaceconcentration in the range of 0.01 μg/cm² and 0.035 μg/cm², and theglass surface is not cytotoxic. In an embodiment the transmission of theglass, uncorrected for reflection losses, over the wavelength range of400 nm to 750 nm is at least 88%. In another embodiment the ratio of thetransmission at 428 nm/650 nm is at least 99%.

In addition the disclosure is thus further directed to a method ofmaking an antimicrobial, chemically strengthened glass articlecomprising providing glass article having a first surface, a secondsurface and a selected thickness between said surfaces, and alkali metalions in the glass; providing a first ion-exchange bath consisting of atleast one alkali metal ion larger that the alkali metal ions in theprovided glass to impart a compressive stress greater than 250 MPa intothe glass; providing a second ion-exchange bath consisting essentiallyof 0.005 wt % to 5.0 wt % silver nitrate, the remainder of the bathconsisting of the at least one of the alkali metal ions in the firstbath; ion-exchanging with the second bath to thereby incorporate saidsilver and said alkali metal ion(s) into at least one of said surfacesto form a glass article having a compressive stress of greater than 250MPa and at least one an antimicrobial, chemically strengthened surface;and wherein the concentration of silver ion on the surface of the glassis in the range of greater than zero to less than 0.047 μg/cm² and thesecond bath ion-exchange time is less than 30 minutes. In one embodimentthe compressive stress is greater than 500 MPa. The second ion-exchangebath consists of silver nitrate in an amount in the range of 0.15 wt %to 10 wt %, and the remainder of the bath is potassium nitrate. In oneembodiment the second bath ion exchange time is less than or equal to 20minutes. In another embodiment the second bath ion exchange time is lessthan or equal to 10 minutes. The provided glass article is selected fromthe group consisting of soda lime glass, alkali aluminosilicate glassand alkali aluminoborosilicate glass articles. In one embodiment theprovided glass is selected from glasses having a composition:

-   -   (a) 60-70 mol % SiO₂; 6-14 mol % Al₂O₃; 0-15 mol % B₂O₃; 0-15        mol % Li₂O; 0-20 mol % Na₂O; 0-10 mol % K₂O; 0-8 mol % MgO; 0-10        mol % CaO; 0-5 mol % ZrO₂; 0-1 mol % SnO₂; 0-1 mol % CeO₂; less        than 50 ppm As₂O₃; and less than 50 ppm Sb₂O₃; wherein 12 mol        %≦Li₂O+Na₂O+K₂O≦20 mol % and 0 mol %≦MgO+CaO≦10 mol %;    -   (b) 64 mol %≦SiO₂≦68 mol %; 12 mol %≦Na₂O≦16 mol %; 8 mol        %≦Al₂O₃≦12 mol %; 0 mol %≦B₂O₃≦3 mol %; 2 mol %≦K₂O≦5 mol %; 4        mol %≦MgO 6 mol %; and 0 mol %≦CaO≦5 mol %, and wherein 66 mol        %≦SiO₂+B₂O₃+CaO≦69 mol %; Na₂O+K₂O+B₂O₃+MgO+CaO+SrO>10 mol %; 5        mol %≦MgO+CaO+SrO≦8 mol %; (Na₂O+B₂O₃)−Al₂O₃≦2 mol %; 2 mol        %≦Na₂O−Al₂O₃≦6 mol %; and 4 mol %≦(Na₂O+K₂O)−Al₂O₃≦10 mol %;    -   (c) 61 mol %≦SiO₂≦75 mol %; 9 mol %≦Na₂O≦21 mol %; 7 mol        %≦Al₂O₃≦15 mol %; 0 mol %≦B₂O₃≦12 mol %; 0 mol %≦K₂O≦4 mol %; 0        mol %≦MgO≦7 mol %; and 0 mol %≦CaO≦mol %;    -   (d) 50 mol %≦SiO₂≦70 mol %; 8 mol %≦Na₂O≦16 mol %; 9 mol        %≦Al₂O₃≦17 mol %; 2 mol %≦B₂O₃≦12 mol %; 0 mol %≦K₂O≦4 mol %; 0        mol %≦MgO≦4 mol %; and 0 mol %≦CaO≦0.2 mol %. wherein the alkali        metal oxides and the alkaline earth metal oxides are modifiers        and the ratio [(mol %≦Al₂O₃+mol % B₂O₃)÷Σ mol %≦modifiers] is        greater than 1, that is:

[(mol % Al₂O₃+B₂O₃)÷Σmol %≦modifiers]>1; and

-   -   (e) SiO₂>50 mol %; 11 mol %≦Na₂O≦25 mol %; 7 mol %≦Al₂O₃≦26 mol        %; o mol %≦B₂O₃≦9 mol %; 0 mol %≦K₂O≦2.5 mol %; 0 mol %≦MgO≦8.5        mol %; and 0 mol %≦CaO≦1.52 mol %; wherein the foregoing are        substantially lithium free.

The method further comprises the step of applying a low surface energycoating to said at least one antimicrobial, chemically strengthenedglass surface, the coating being selected from the group consisting offluoroalkylsilanes, perfluoropolyether alkoxy silanes, perfluoroalkylalkoxy silanes, fluoroalkylsilane-(non-fluoroalkylsilane) copolymers,and mixtures of fluoroalkylsilanes and hydrophilic silanes; and curingthe applied coating to thereby bond the coating to the glass by a Si—Obond between the coating and the glass; wherein the functional coatinghas a thickness in the range of 0.5 nm to 20 nm. In one embodiment thelow surface energy functional coating is a perfluoroalkyl alkoxy silaneof formula (R_(F1))_(x)—Si(OR)_(4-x), where x=1 or 2, R_(F1) moiety is aperfluoroalkyl group having a carbon chain length in the range of 16-130carbon atom and OR is acetoxy, —OCH₃ or OCH₂H₃. In another embodimentthe low surface energy functional coating bonded to the antimicrobial,chemically strengthened glass is a perfluoropolyether alkoxy silane offormula [CF₃—(CF₂CF₂O)_(a)]_(x)—Si(OR)_(4-x) where a is in the range of5-10, x=1 or 1, and OR is acetoxy, —OCH₃ or OCH₂H₃, wherein the totalperfluoroether chain length from the silicon atom to the end of thechain at its greatest length its end is in the range of 1 nm to 10 nm,16 to 130 atoms. In a further embodiment the low surface energyfunctional coating bonded to the antimicrobial, chemically strengthenedglass is a perfluoroalkyl alkyl alkoxy silane of formula[R_(F2)—(CH₂)_(b)]_(x)—Si(OR)_(4-x) where R_(F2) is a perfluoroalkylgroup having a carbon chain length in the range of 10-16 carbon atoms, bis in the range of 14-20, x=2 or 3 and OR is acetoxy, —OCH₃ or OCH₂CH₃.In one embodiment the low surface energy functional coating is appliedto form domains on the surface of the glass and a non-domain areawithout coating. In another embodiment the low surface energy applieduniformly/continuously across the glass surface and has a thickness inthe range of 0.5 nm to 10 nm. In one embodiment the thickness in therange of 1 nm to 3 nm. The method produces as glass having atransmission of the glass, uncorrected for reflection losses, over thewavelength of 400 nm to 750 nm is at least 88%., and also the ratio ofthe transmission at 428 nm/650 nm is 99%.

For use as antimicrobial shelving, table tops and other applications inhospitals, laboratories and other institutions handling biologicalsubstances, where color in the glass is not a consideration, glasshaving a silver ion surface concentration of greater than 0.035 μg/cm²may be suitable. Glass having a silver ion surface concentration of 0.5or higher may be prepared using the methods described herein.

While typical embodiments have been set forth for the purpose ofillustration, the foregoing description should not be deemed to be alimitation on the scope of the disclosure or the appended claims.Accordingly, various modifications, adaptations, and alternatives mayoccur to one skilled in the art without departing from the spirit andscope of this disclosure or the appended claims.

We claim:
 1. An antimicrobial glass comprising: a glass article having asurface; an antimicrobial Ag+ region extending from the surface of theglass article to a depth in the glass article, the Ag+ region having aplurality of Ag⁺¹ ions, wherein the concentration of the plurality ofAg⁺¹ ions on the surface of the glass article is in the range of greaterthan zero to less than or equal to 0.08 μg/cm².
 2. The antimicrobialglass of claim 1, further comprising a compressive stress layer having acompressive stress of at least 250 MPa.
 3. The antimicrobial glass ofclaim 1, wherein the glass is colorless.
 4. The antimicrobial glass ofclaim 1, wherein the depth of the antimicrobial Ag+ region is about 20μm or less from the surface.
 5. The antimicrobial glass of claim 1,wherein the concentration of the plurality of Ag⁺¹ ions is about 3.22atomic % or less extending from the surface of the glass article to adepth of about 5 nm.
 6. The antimicrobial glass of claim 1, wherein thedepth of the antimicrobial Ag+ region is about 1 μm or less from thesurface.
 7. The antimicrobial glass of claim 1, wherein theconcentration of the plurality of Ag⁺¹ ions on the surface of the glassarticle is in the range of greater than zero to less than or equal to0.05 μg/cm².
 8. The antimicrobial glass of claim 1, further comprising ahydrophobic coating.
 9. The antimicrobial glass of claim 8, wherein thehydrophobic coating has a thickness in the range from about 0.5 nm toabout 20 nm.
 10. The antimicrobial glass of claim 8, wherein thehydrophobic coating comprises one of a discontinuous coating and acontinuous peak-to-valley coating, and wherein the continuouspeak-to-valley coating comprises at least one peak having a firstthickness and at least one valley having a second thickness less thanthe first thickness.
 11. The antimicrobial glass of claim 1, wherein thecomposition of the glass article is selected from the group consistingof soda lime glass, alkali aluminosilicate glass and alkalialuminoborosilicate glass.
 12. A device comprising the glass article ofclaim
 1. 13. The device of claim 12, wherein the device comprises anATM, a touch screen computer, a cellphone, or an electronic book reader.14. An antimicrobial glass comprising: a glass article; an antimicrobialAg+ region extending from the surface of the glass article to a depth ofregion in the glass article, the Ag+ region having a plurality of Ag⁺¹ions, wherein the concentration of the plurality of Ag⁺¹ ions on thesurface of the glass article is in the range of greater than zero toless than or equal to 0.08 μg/cm², and wherein the antimicrobial Ag+region comprises a concentration of Ag₂O of up to about 25 wt % from thesurface of the glass article.
 15. The antimicrobial glass of claim 14,wherein the concentration of Ag₂O is up to about 19 wt %.
 16. Theantimicrobial glass of claim 14, further comprising an abraded Ring onRing of about 380 MPa or greater.
 17. The antimicrobial glass of claim16, wherein the depth of region is up to about 20 μm.
 18. A devicecomprising the glass article of claim
 14. 19. The device of claim 18,wherein the device comprises an ATM, a touch screen computer, acellphone, or an electronic book reader.
 20. The device of claim 18,wherein the glass article further comprises a hydrophobic coating.